A technology is known in which a high speed serial link is used for a connection between nodes of a large-scaled computer. It is known that in a case of a PCI (Peripheral Components Interconnect) Express or 10 GbE (Gigabit Ethernet (registered trademark)), a power consumed by a physical layer of the high speed serial link is an order of 20 mW per 1 Gbps. In the future, in a case where a countermeasure that increases the number of lanes per link is established in order to enhance a link speed, the power consumed by a physical layer of the high speed serial link is increased and becomes non-negligible.
In the large-scaled computer, a program may be executed in which a computation phase of performing a computation after receiving data and a communication phase of transferring the computation result to other node are alternately repeated. In this case, in the computation phase, an idle pattern is sent and received between the node counterparts such that unnecessary electrical power is consumed so as to maintain the established link in the high speed serial link. That is, an operation state is maintained even when a data transfer is not accompanied and thus an electrical power is consumed. When it is intended to suppress the unnecessary power consumption, an operation of the serial link needs to be stopped during the computation phase, but it may take several microseconds for a startup time (activation time) to recover from a stopped state (OFF) to an operation state (ON). Therefore, when the operation of the link is simply stopped, the startup time required for the recovery is added to a communication delay time and a computational efficiency is reduced.
In the meantime, in Japanese Laid-Open Patent Publication No. 2011-123798 or Japanese Laid-Open Patent Publication No. 2011-199361, a technology is disclosed in which the number of lanes is dynamically controlled according to the number or amount of messages that pass through the link per unit time. However, a significant time is required for switching a power supply of the lane from an OFF state to an ON state and thus, even though the number of lanes is dynamically controlled simply according to the number or amount of messages, there is no guarantee that communication may be performed at a timing at which a sufficient bandwidth may be utilized. There may be a case where most of communications have been completed at a time when all the lanes start up. Accordingly, also in Japanese Laid-Open Patent Publication No. 2011-123798 or Japanese Laid-Open Patent Publication No. 2011-199361, when the operation of the link is simply stopped, the startup time taken for the recovery is added to the communication delay time and the computational efficiency is reduced.
In Japanese Laid-Open Patent Publication No. 2010-283696, a technology in which the number of lanes is changed according to a connection communication protocol. This is because the number or amount of communications in a connectionless protocol such as a SNMP (Simple Network Management protocol) or ARP (Address Resolution Protocol) does not influence on the variation of the number of lanes. The number of lanes varies according to a data size used by an application. However, the turn ON/OFF time (startup time) of the power supply of the lane is not considered in the Publication No. 2010-283696. Accordingly, also in Japanese Laid-Open Patent Publication No. 2010-283696, when the operation of the link is simply stopped, the startup time taken for the recovery is added to the communication delay time and the computational efficiency is reduced.
In Japanese National Publication of International Patent Application No. 2008-547362, a technology in which increase or decrease of a link speed or a link bandwidth is dynamically negotiated in response to a command under a software control, but the turn ON/OFF time (startup time) of the power supply of the lane (startup time) is not considered. Accordingly, also in Japanese National Publication of International Patent Application No. 2008-547362, when the operation of the link is simply stopped, the startup time taken for the recovery is added to the communication delay time and the computational efficiency is reduced.
Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2011-123798, Japanese Laid-Open Patent Publication No. 2011-199361, Japanese Laid-Open Patent Publication No. 2010-283696, and Japanese National Publication of International Patent Application No. 2008-547362.